Localized heating filaments by induced currents

ABSTRACT

A method and apparatus is disclosed for using a plurality of spaced sequential induction circuits for inducing a predetermined current distribution pattern in a localized segment of a filament. The induced current pattern is controlled by combining the effects of electro-magnetic induction, and standing wave patterns on the filamentary conductor together with the transmission attenuation along the filamentary conductor. Additionally, the effect of the configuration of an induction circuit on induced current is covered.

United States Patent [191 DeBolt [111 3,754,112 Aug. 21, 1973 [541 LOCALIZED nenmc FILAMENTS BY mnucen CURRENTS [75] Inventor: Harold E. DeBolt, Andover, Mass.

[73] Assignee: Avoo Corporation, Cincinnati, Ohio [22] Filed: June 14, 1972 [21] Appl. No.: 262,749

[52] US. Cl 219/10.61, 117/107.2, 118/495,

219/1071, 219/10.81 [51] Int. Cl. 1105b 9/02 [58] Field of Search 219/10.61, 10.55,

2,320,801 6/1943 Simons 219/1061 X 2/1970 Ross 219/1079 X 6/1968 Hough 118/495 X OTHER PUBLICATIONS Powell et al., Vapor Plating," John Wiley and Sons, N.Y., N.Y., 1955, pp. 71-77, 95, 96, 103-106.

Primary Examiner.1. V. Truhe Assistant Examiner-43. A. Reynolds Attorney-Charles M. Hogan and Abraham Ogman et a1.

[ 5 7] ABSTRACT A method and apparatus is disclosed for using a plurality of spaced sequential induction circuits for inducing a predetermined current distribution pattern in a localized segment of a filament. The induced current pattern is controlled by combining the effects of electromagnetic induction, and standing wave patterns on the filamentary conductor together with the transmission attenuation along the filamentary conductor. Additionally, the effect of the configuration of an induction circuit on induced current is covered.

12 Claims. 4 Drawing Figures Patented Aug. 21, 1973 2 Sheets-Sheet 1 Fill 1 LOCALIZED HEATING FILAMENTS BY INDUCED CURRENTS The theory and mechanism of heating filaments bymeans of induction currents is well known and fully documented in the specification and file wrapper of limited region of the filament is. heated. Additionally,v

there is no provision for providing; localized heating at selected regions. along the filament. Further, the patented configuration includes. no. provision for shaping the; induced current distribution along the filament,

length. 1

Though in one respect this invention operates in a manner similar to the patented: invention, this-invention concept avoids limitations discussed just above- Though. the preferred embodiment relates to au-xils iary localized heating where the primary heat source is DC or utility AC? power, the invention concept may be used as the principal heat source. The latter procedures.

will depend largely on economics.

The invention has. particular application to the manu- I facture of high-strength and? high modulus carbon, boron and? silicon carbide filaments, for example.

lt is an object. of the invention tov provide a methodand. apparatus; for providing localized heating of filjaments. which avoids: the limitations; and disadvantages. of prior inventions and? apparatus.

It is another object, of the. inventionto provide a method and apparatus: for providing localized heating of filaments by combining the effects of induced cur- ,rents: produced by two. or more. induction circuits.

lt is still another object of'the; invention to provide a means. for inducing a predetermined current. distribution pattern. in a localized. segment ofafilament.

lt is. yet another object of the. invention; to controlinduced' current distribution patterns. by combining. the. efifects; of electro-magnetic induction and? standing;

wave patte-ns on. the filamentary conductor;

It is yet another object ofthe invention. to. disclose a meansv for modifying an: induced current distribution pattemby modifying: the. configuration of the. induction:

circuit. A method. of resistance lieatinga; filament comprises .the: steps of establishing. at least. a: pair of induction circuits, each. ofiwhich induces current in a filament. The induced cur-rents; interactv to form predetermined current. distribution patterns;

The. novel. features; that. are considered. characteristic of? the: invention: are; sets. forth in. the. appended claims; the invention itself, however,v both: as: to. itsorganizati'on and: method of operation, together with additional ob jects'. and? advantages. thereofl. will best be understood trom: the following description. of a specific embodiment: whenread in; conjunction with the; accompanying drawings, in: which: FIG... 1 is a schematic. representationzof an: apparatus for manufacture; of high: modulus filaments which. em-

bodies: the: principal. of? the present invention; and.

- 1 FIGS. 2A through; 2C are idealizedi schematic representations of'an alternate apparatus configuration.v

ally, afilamentary substrate such as tungsten, molybde num, or carbon wire is supplied by means of a reel 11 through an electrical contact 12 and passes through the length of the reactor 10 to a second electrical contact 13 to a take-up reel 14.

Typically, the coating material is obtained by thermally decomposing a gas flowing through the reactor 10; The gas: enters by way of conduit 16, passes through the reactor and out through a conduit 17 to a recovery system. to be recycled. In the event boron is to be deposited on. the filament substrate, the gas is. a boron halide, generally boron trichloride. Where silicon carbide is to. be deposited, analkyl silane is. generally used. These gases are also generally mixed with hydrogen to provide a reducing atmosphere.

Similarly, TiB, may be deposited from TiCl, and BCL, with hydrogen; or 8 C from BCl; with a hydrocarbon. or B'N. from BC], and tn'chloroborazole. The localized heating should also work in reactors: designed'for depositing TaC, and TiC from a vapor phase or for con v'erti'ng a carbon filament into a high modulus graphite filament.

Typically, the substrate filament 18 is heated by passing. DC current through the filament by means of contacts l2 and: 13.. The substrate filament is heated to a temperature which is sufficient to. cause the reagent gas to decompose. and deposit a coating on the surface: of the. substrate; boron or silicon carbide for the gases specified.

A very, serious problem: associated with. the basic coating technique just described is; that the resistance perunit length of the filament varies with the length be cause the amount of material deposited-thethickness of" the coating-on* the substrate filament. increasesas the: substrate filament passes through the: reactor. As a result, the filament temperature. varies as. a function: of distance. through the reactor. Most oftenthe temperature falls off more rapidly tharr desired as the filament passes through the. reactor. Frequently localizedheating is sought to make the temperature: profile more nearly constant. Temperature controlz may be obtained bycoolingnormally hotter regionseor conversely, heat. can: be: supplied" to a: cooler region. to. bring the-temperature up. The subject oiithisinvent ion isdirected' to-such.

auxiliary heating by means. of inducing: current in. the filament,.and; in: particular, to localizedi auxiliary heat ing.

Referring to FIG- 1, there is. shownv a number of in:- duction circuits. along the: length of the filament 18 Each. induction. circuit induces a current in a localized region of the filament by electromagnetic induction.

Preferably; the induction circuits are supplied with VHF energy in the 1.0:mhzto mhz range; forexample.

Induction. circuit 21 comprises an. L-shaped wire inductance 22 "v connected in: series with. a capacitor 23-. The wall 24. of the reactor 1.0 is an RF ground,v as indicated. Typically,. the. induct-ionqcircuit 21' is coupled to a. source. of VHF energy" (not shown")- by' means of'the coupling means 26. Preferably, the: series inductance One leg 27 of the inductance 22 extends parallel and is spaced from the substrate filament 18. The terminal end 29 preferably, but any point along the inductanceof the leg 27 is connected to the capacitor 23. The op posite end of the leg 27 terminates in the corner of the L-shaped inductance 22. The terminal end 29 is a high electric field region. The electromagnetic field is coupled to the substrate filament 18 and induces within the substrate filament 18 a localized current in the region of the substrate filament 18 adjacent to the terminal end 29. The electric field gradient is generally axially disposed so that, in this case, the current induced in the substrate filament 18 is axial.

The strength of the electric field at the corner of leg 27 is somewhat less than at the terminal end 29. As one would expect, current in the inductance at the corner of leg 27 is somewhat higher; the current is maximum at the terminal end 30 of leg 27. The electromagnetic field in the vicinity of the corner induces a current in the substrate filament 18 in the region opposite the corner.

A graphical representation of the currents induced by the several induction circuits shown in FIG. 1 is illustrated by a plurality of curves. The curves represent the magnitude of current as a function of length along the substrate filament 18, as indicated.

The current maximum 32 and 33 arise because of the change in transmission characteristics of the conducting filament 18 as a result of the proximity of the conductor of the tuned circuit. Within the region near the tuned circuit, the characteristic impedance of the conducting filament 18 is lower than it is outside this region. At this point of discontinuity, the standing wave current distribution is altered by wave reflections at the discontinuity, in the higher impedance sections outside the tuned circuit. The reflection reinforces the oncoming wave, and in the lower impedance region within the coupling loop, the reflection at the discontinuity is out of phase with the main induced wave. As a result, a current maximum occurs outside the region where the tuned coupling loop is located.

Curve 31 represents the current distribution induced in the substrate filament 18 by the tuned circuit 21. The small peak 32 is adjacent the corner leg 27. The large peak is opposite the terminal end 29. The relative magnitudes of the peaks 32 and 33 will vary, particularly as the length of the leg 27 is changed.

The next region of interest comprises a tuned circuit 41 and an adjacent loop 42. Curve 43 represents the current distribution in the selected region in the substrate filament derived from the tuned circuit 41. Curve 44 represents the current distribution in the substrate filament generated by the loop 42. The loop 42 prov duces a predominantly electromagnetic field. Since the loop 42 is not coupled to the VHF supply means, the

I energy contained in loop 42 is derived from energy coupled to loop 42 from the tuned circuit 41. A single current peak 44 is derived from the loop 42. Curve 46 is composite representing the actual current distribution in the region caused by the combined effects of curves 43 and 44. Further down the reactor 10 are three tuned circuits 5], 52 and 53. Current distribution 54 is generated by tuned circuit 51. Current distribution 56 is generated by tuned circuit 52. And, current distribution 57 is generated by tuned circuit 53. Curve 59 is the composite actual current distribution in the substrate filament 18 in the specific region generated plicity of tuned coupling circuits, each as short as necessary to keep the variation of current along the fila ment to be heated as desired. In practice, however,"

these closely spaced tuned circuits also couple with each other as well as with the filament to be heated, making difficult the task of tuning the group of tuned circuits. A method to reduce the complexity of multiple coupling loops is shown in tuned circuit 53 where the leg 58 is bent with a concave portion 60. The portion of the tuned circuit bent away from the heated filament causes reflections exactly the same as those beyond the ends, causing an additional current maximum within the tuned circuit region. By using this additional feature of perturbing the shape of each tuned circuit, one can obtain the same effect with fewer (perturbed) tuned circuits as could be obtained with many more shorter unperturbed units.

Conceptually therefore, a means is provided for modifying the normal current distribution patterns of tuned circuits by altering the configuration of the inductance of the tuned circuit in the region running parallel with the filament to be heated. Referring to curve 59 and particularly the region between tuned circuits 51 and 52, it is seen that the curve drops, typically, to a low level of current in the region between points C and D. Because the magnitude of current represented by curve 54 and 56 falls off rapidly between A and B.

On the other hand, the effect of the double peaks 61 and 62 in curve 57 providing a heated boost in current in the region between points C and D tendiiig to develop a current plateau in that region of the composite curve 59. The dotted curve 60 represents the drop in current that would have occurred in the absence of C.

FIG. 2 contains schematic representations of placing a pair of tuned circuits side-by-side with their respective predominantly high voltage regions in an adjacent relationship. In FIG. 1, a high electric field region was located next to a region of lesser electric field. In FIG. 2, the current induced with a substrate filament results primarily from the interaction of the adjacent high electric fields. Curve 71 is generated by tuned circuit 72. Curve 73 is generated by tuned circuit 74. Current circuit 75 is the composite of 71 and 73. Note that current curve 75 is a single relatively sharp peak.

In FIG. 2b the tunedcircuits 76 and 77 are spaced further apart than their counterparts in FIG. 2a. The composite current curve 81 represents the combined effects of the individual curves 82 and 83 and a single peak. Significant is that this peak is more rounded off than the peak in the composite curve 75.

Where the tuned circuits are even more widely spaced as shown in FIG. 20, the composite current distribution curve 84 contains a plurality of peaks, and ex.- tends over a greater length of the substrate filament 18.

The various features and advantages of the invention are thought to be clear from the foregoing description.

Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in theart, as-likewise will many variations and modifications of-the preferred embodiment illustrated, all of which 'may' be achieved without departing from the spirit and scope of the invention as defined by the following claims.

I claim:

1. Means for inducing a predetermined point .to point current distribution in a localized segment of a filament comprising:

at least a pair of induction circuits disposed in a spaced relationship along the length of said filament, each of said induction circuits inducing localized current in a localized region of said filament, said localized currents interacting to produce a predetermined composite current distribution.

2. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 1 wherein said induction circuits consist essentially of tuned circuits, as loops, modified tuned circuits, modified loops or combinations thereof.

3. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 1 wherein at least one of said induction means produces axially spaced impedance discontinuities, said discontinuities inducing currents having standing waves that generate axially spaced current peaks in said filament in a localized region opposite each discontinuity.

4. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 3 wherein said one induction circuit is a tuned circuit.

5. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 3 wherein said tuned circuit comprises an L-shaped inductance with one leg of the inductance extending parallel to said filament, the terminal end and the comer of said one leg causing impedance discontinuities.

6. Means for inducing a predetermined point tp point current distribution in a localized segment of a filament as defined in claim 5 wherein the spacing between said one leg and said filament is varied to induce additional localized impedance discontinuities in the region of current distribution in a localized segment of a filament as defined in claim 3 wherein adjacent induction means inducing currents are disposed with the region of maximum electric field of one induction circuit positioned adjacent to the region of maximum electric field of another induction circuit.

9. A method of heating a filament comprising the steps of:

inducing a predetermined point to point localized current in a localized region of said filament by the combination of electromagnetic induction and the introduction of axially spaced impedance discontinuities by at least two induction circuits consisting essentially of tuned circuits, as loops, modified tuned circuits, modified loops or combination thereof.

10. In a method whereby a carbon filament is heated near or at graphitizing temperatures, the improvement comprising supplying localized heat by inducing two or more axially spaced and predetermined point to point localized currents in a localized region of the carbon filament to add heat to said carbon filament locally.

11. A method of making a high-strength highmodulus filament comprising the steps of:

a. providing a substrate filament into which currents can be induced;

b. drawing the substrate filament through a reactor containing vapors which react at elevated temperatures to deposit boron or SiC on a heated substrate, said filaments being heated along its entire length by a first source of heat; and

c. supplying localized heat by inducing two or more axially spaced and localized currents in a localized region of the substrate filament.

12. A method of making a high-strength highmodulus filament comprising the steps of:

a. providing a substrate filament into which currents can be induced;

b. drawing the substrate filament through a reactor containing vapors which react at elevated temperatures to deposit a coating taken from the class consisting essentially of'TiB B C, BN, TiC or TaC on a heated substrate, said filaments being heated along its entire length by a first source of heat; and

. supplying localized heat by inducing two or more axially spaced and localized currents in a localized region of the substrate filament.

it)??? UNITED "PATENT OFFICE v CERTIFICATE F CORRECTION I Patent NO 35 75451112, Dated Aligllst 21; 71 973 e Inventofl s) I I .HArR OLD E. DeBCLT It is certified that error appears in the above-identified parent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 6; fo FU, s. Pat. No.3, 60?, 603;", r ad ---U. 5, Pat, No; 3, 607, O63?---1- and C01. 1, line 45' for pattens" readpatterns v Y I Signed and se'a led'thi s 25 th day of Deeejmber 1973.

(SEAL) AttSt Z EDWARD M.FLETCHER,IJR, l RENE D. TEGTMEYER v Att est ingOffiie'r r '-Act1ng 'COITIIIIlS'Sl'OQGI of Patents #3 3 93 EINE'KED STATES PA'IENT OFFICE v EERTWECATE Oi CORRECTION Patent No. 3, 75%, 112v Dated August 21; 1973 Inventor(s) HAROLD E. DeBOLT It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col, 1, line 6, for "us. Pat. No. 3,607,603", read ---U.S, Pat. No. 3,607, 063 and Col. 1, line 45 for pattens, read patterns Signed and sealed this 25th day of December 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. RENE D. TEGIMEYER Acting Commissioner of Patents Attesting Officer 

1. Means for inducing a predetermined point to point current distribution in a localized segment of a filament comprising: at least a pair of induction circuits disposed in a spaced relationship along the length of said filament, each of said induction circuits inducing localized current in a localized region of said filament, said localized currents interacting to produce a predetermined composite current distribution.
 2. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 1 wherein said induction circuits consist essentially of tuned circuits, as loops, modified tuned circuits, modified loops or combinations thereof.
 3. Means for inducinG a predetermined point to point current distribution in a localized segment of a filament as defined in claim 1 wherein at least one of said induction means produces axially spaced impedance discontinuities, said discontinuities inducing currents having standing waves that generate axially spaced current peaks in said filament in a localized region opposite each discontinuity.
 4. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 3 wherein said one induction circuit is a tuned circuit.
 5. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 3 wherein said tuned circuit comprises an L-shaped inductance with one leg of the inductance extending parallel to said filament, the terminal end and the corner of said one leg causing impedance discontinuities.
 6. Means for inducing a predetermined point tp point current distribution in a localized segment of a filament as defined in claim 5 wherein the spacing between said one leg and said filament is varied to induce additional localized impedance discontinuities in the region of said filament between the terminal end and said corner.
 7. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 3 wherein adjacent induction means inducing currents are disposed with the maximum electric field of one induction circuit positioned adjacent to a region of lesser electric field of another induction circuit.
 8. Means for inducing a predetermined point to point current distribution in a localized segment of a filament as defined in claim 3 wherein adjacent induction means inducing currents are disposed with the region of maximum electric field of one induction circuit positioned adjacent to the region of maximum electric field of another induction circuit.
 9. A method of heating a filament comprising the steps of: inducing a predetermined point to point localized current in a localized region of said filament by the combination of electromagnetic induction and the introduction of axially spaced impedance discontinuities by at least two induction circuits consisting essentially of tuned circuits, as loops, modified tuned circuits, modified loops or combination thereof.
 10. In a method whereby a carbon filament is heated near or at graphitizing temperatures, the improvement comprising supplying localized heat by inducing two or more axially spaced and predetermined point to point localized currents in a localized region of the carbon filament to add heat to said carbon filament locally.
 11. A method of making a high-strength high-modulus filament comprising the steps of: a. providing a substrate filament into which currents can be induced; b. drawing the substrate filament through a reactor containing vapors which react at elevated temperatures to deposit boron or SiC on a heated substrate, said filaments being heated along its entire length by a first source of heat; and c. supplying localized heat by inducing two or more axially spaced and localized currents in a localized region of the substrate filament.
 12. A method of making a high-strength high-modulus filament comprising the steps of: a. providing a substrate filament into which currents can be induced; b. drawing the substrate filament through a reactor containing vapors which react at elevated temperatures to deposit a coating taken from the class consisting essentially of TiB2, B4C, BN, TiC or TaC4 on a heated substrate, said filaments being heated along its entire length by a first source of heat; and c. supplying localized heat by inducing two or more axially spaced and localized currents in a localized region of the substrate filament. 